Whalefall by Daniel Kraus

Jay Gardiner has set out on a fool’s errand: Find the remains of his deceased father in the Pacific Ocean off the coast of Monastery Beach. He knows it’s a long shot but feels it’s the only way to relieve the guilt he has carried since his dad’s suicide the previous year. The dive begins well enough, but the sudden appearance of a giant squid puts Jay in jeopardy, made infinitely worse by the arrival of a sperm whale looking to feed. Suddenly Jay is caught in the squid’s tentacles, then pulled into the whale’s mouth and the first of its four stomachs. He quickly realizes he has only one hour before his oxygen tanks run out—one hour to defeat his demons and escape the belly of a whale.